This invention relates in general to bearings and more particularly to rotary air bearings and processes for manufacturing the same.
In some equipment rotors revolve at extremely high velocities, yet with considerable precision. For example, the disk in the disk drive of a computer rotates at a high velocity to facilitate rapid storage and retrieval of information, but the disk must also run true both axially and radially. Indeed, the disk must be essentially free of nonrepetitive runout and error in motion (wobble). This insures that the tracks on the disk remain precisely in the same position and prevents the heads which read the disk from scraping the disk. Rotary mirrors for optical scanners must likewise rotate at high velocities with high precision. The same holds true with regard to the rotors in gyroscopes.
To a measure ball bearings have accommodated the demands of such equipment. But as the velocity and precision with which such equipment operates increases, the capability of ball bearings to satisfy these demands has diminished. The typical ball bearing used in rotary applications includes inner and outer races with rolling elements in the form of balls located between the races. When one race rotates relative to the other, the balls roll along raceways on the two races. The rolling contact keeps friction minimal. Even so, geometric inaccuracies in the balls and the raceways may translate into motions that occur at nonintegral fractions of spinspeed and thus do not lend themselves to compensation. This is detrimental to the operation of the equipment. Moreover, they set up vibrations which in their own right are detrimental. Furthermore, ball bearings require lubricants which may migrate into regions where they will adversely affect the operation of the equipment.
So-called air or gas bearings accommodate extremely high velocities with considerable precision, and thus overcome the primary deficiencies of ball bearings. In that sense they are well-suited for high speed equipment such as disk drives and optical scanners, but they have not found favor with the manufacturers of such equipment because of the extremely close tolerances required in the manufacture of such bearings and the expense required to maintain those tolerances.
The typical air bearing includes a journal and a hub, one of which revolves with respect to the other. Sometimes a small electric motor is integrated into the journal and hub to effect the rotation. The journal and hub have matching surfaces which, during the operation of the bearing, are separated by a thin layer of air. Hence, the surfaces do not contact each other and essentially no friction exists to impede the rotation. The air for the film may come from an external source (hydrostatic) or it may derive from the rotation itself (hydrodynamic). Bearings which operate on the latter principle normally have grooves to elevate the pressure in the air gap between opposed thrust-oriented surfaces. Such bearings are referred to as self-acting bearings.
In one configuration the self-acting air bearing has its opposed thrust-oriented surfaces tapered down from each end toward the mid-region of the bearing. The tapers, in effect, capture the hub on the journal, but this presents manufacturing problems. In this regard, the tapered regions of the journal are normally manufactured separately and then assembled within the hub. Since the two tapered regions are not machined on the same center, the possibility exists that their axes may not coincide precisely as they must when assembled in the hub. This produces error in motion. Then there is the usual problem of maintaining roundness and consistency between the matching tapered surfaces of the journal and hub, not to speak of a uniform air gap on the order of 50 to 100 microinches.
These demands require precision machining and grinding and even lapping which is reflected in the price of such bearings, making them considerably more expensive than conventional ball bearings. Hence, most of the high velocity equipment uses traditional ball bearings.
The present invention resides in an air bearing having opposed tapered surfaces, one of which lies along a material that is molded along the other surface and then separated slightly from the other surface. The invention also resides in the process for manufacturing a bearing. That process includes providing inner and outer members, one of which has tapered surfaces and using those tapered surfaces to configure and provide conforming tapered surfaces for a liner that lies between the members and bonds to the other member. Actually, the liner is derived from a fluent liner material which is injected between the inner and outer members. But before the fluent liner material is injected, the tapered surfaces on the one member are distorted in the sense that they are displaced axially. This distortion may be achieved by compressing the one member within its elastic limits or by applying a coating to the tapered surfaces. Once the liner material has solidified the distortion is removed, leaving a slight air gap between the tapered surfaces on the one member and the conforming tapered surfaces on the liner. The member with the tapered surfaces or the liner along their tapered surfaces has grooves which serve to pump air and thereby maintain the air gap generally uniform. The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.